I'm running the Windows build of 5.0.2 on 32bit Windows 7 and I've run into the following issues with sine and cosine. Here is a paste of my interaction with Racket: > (inexact->exact (sin 0)) 0 ; fine > (inexact->exact (cos 0)) 1 ; fine > (inexact->exact (sin (/ pi 2))) 1 ; fine > (inexact->exact (cos (/ pi 2))) 0.0000000000000000612323399... ; should be 0 > (inexact->exact (sin pi)) 0.0000000000000001224646799... ; should be 0 > (inexact->exact (cos pi)) -1 ; fine > (inexact->exact (sin (* 3 (/ pi 2)))) -1 ; fine > (inexact->exact (cos (* 3 (/ pi 2)))) -0.0000000000000001836970198... ; should be 0 > (inexact->exact (sin (* 2 pi))) -0.0000000000000002449293598... ; should be 0 > (inexact->exact (cos (* 2 pi))) 1 Granted it is a very small amount to be off by and I doubt it's throwing off my answers at all (working on exercise 27.1.4) just thought you should be aware of it.